Two new projects have been initiated to determine the (1) the genes and/or gene products altered in asbestos transformed human mesothelial cells and (2) the chromosomal localization of the hepatitis B core antigen gene introduced into human lung carcinoma cells. In addition, we have determined that a diol-epoxide of benz(a)anthracene introduces single-strand breaks in DNA at guanidine and adenosine residues. The reactivity of specific bases is different if the same sequence is reacted as double-stranded or single-stranded DNA.